In the pharmaceutical industry, a machine for filling capsules with a pharmaceutical product in granules is known comprising a conveyor device movable continuously along a given path and having a number of pockets, each for receiving a respective bottom shell of a capsule; at least one tank containing the product; and a metering wheel mounted to rotate continuously about its substantially vertical longitudinal axis.
The metering wheel has a number of metering devices, each of which travels with the metering wheel along a portion of the path of the bottom shells, in time with a respective bottom shell, to transfer a given quantity of product from the tank into the bottom shell.
Each metering device comprises a substantially cylindrical metering chamber for receiving the product from the tank; an unloading chute for unloading the product from the metering chamber into the relative bottom shell; and a piston, which defines the bottom of the metering chamber, and is moved along the metering chamber, by a cam follower roller engaging a cam associated with the metering wheel, to and from a feed position to feed the product to the unloading chute and, therefore, into the bottom shell.
Each pocket on the conveyor device is defined by a shaped bush with a capacitive transducer, which provides for weighing the respective empty bottom shell, weighing the respective bottom shell containing the product, and calculating the weight of the product in the respective bottom shell as the difference between the two weights.
Known machines of the type described above have various drawbacks, mainly due to the fact that, though amply tried and tested, the method used to calculate the weight of the product in each bottom shell fails to prevent a possible error in the weight of the bottom shell from impairing calculation of the weight of the product in the bottom shell, particularly in view of the high dielectric constant of the material of the bottom shell with respect to the dielectric constant of the product inside the bottom shell.